Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds two useful facts beyond that: the data is public (no auth implied) and results come back in the requested language, but it says nothing about what the comparison contains or how it behaves on invalid input.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

One sentence, front-loaded with the verb and resource, with no filler. It is arguably a touch too terse given the missing usage guidance, but nothing in it is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple two-parameter read tool this is close to adequate, and the annotations carry the safety burden. However, with no output schema the description should at least sketch what a 'feature comparison' returns and confirm behavior when a plan or locale is unavailable.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 50%: the locale parameter is documented, but plans is not. The description's 'two or three Semly plans' and 'in the requested language' merely restate the schema's minItems/maxItems and locale field, without explaining valid plan choices beyond the enum or what happens with a missing locale.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: 'Read the public feature comparison of two or three Semly plans.' That is concrete enough to distinguish it from siblings like get_offers or search_content, though it never names those alternatives explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no when-to-use or when-not-to-use guidance. The description does not say when an agent should call compare_plans versus get_offers, nor does it mention prerequisites or failure cases such as an unsupported plan/locale combination.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.